1. Field of the Invention
The present invention relates to a radiation imaging apparatus, a control method for the radiation imaging apparatus, a storage medium, and, more particularly, to a radiation imaging apparatus that reduces image artifacts upon imaging an object by intermittently irradiating the object with radiation in the form of pulses, a control method for the radiation imaging apparatus, and a storage medium.
2. Description of the Related Art
Recently, in the field of radiation imaging apparatuses, especially, digital X-ray imaging apparatuses, a large-area flat panel type radiation imaging apparatus based on a 1× optical system using photoelectric conversion elements has been widely used, instead of an image intensifier, for the purpose of increasing resolution, decreasing volume, and suppressing image distortion.
A large-area flat panel sensor formed by two-dimensionally joining photoelectric conversion elements generated on a silicon semiconductor wafer by a CMOS semiconductor manufacturing process is available as a flat panel sensor based on a 1× optical system that is used for a radiation imaging apparatus.
Japanese Patent Laid-Open No. 2002-026302 discloses a method of manufacturing a large-area flat panel sensor by tiling a plurality of rectangular semiconductor substrates that are rectangular imaging elements obtained by cutting photoelectric conversion elements in the form of strips from a silicon semiconductor wafer, in order to implement a large-area flat panel sensor equal to or larger than the silicon semiconductor wafer size.
In addition, Japanese Patent Laid-Open No. 2002-344809 discloses a circuit arrangement for each rectangular semiconductor substrate obtained by cutting out photoelectric conversion elements in the form of strips. On each of the rectangular semiconductor substrates cut out in the form of strips, vertical and horizontal shift registers as readout control circuits are arranged together with two-dimensionally arrayed photoelectric conversion elements. External terminals (electrode pads) are provided near the horizontal shift register. Control signals and clock signals input from the external terminals control the vertical and horizontal shift registers on each rectangular semiconductor substrate to cause the respective shift registers to sequentially output the respective pixel arrays in synchronism with the clock signals.
For example, as shown in FIG. 5A, no significant problem occurs when the sum of a scanning time ST required to output electrical signals from all of the photoelectric conversion elements and a radiation signal accumulation time XT (exposure time XT) is less than an imaging interval FT of a synchronization signal, that is, the frame rate is relatively low.
FIG. 5B shows an example of an imaging mode in which the sum of the scanning time ST required to output electrical signals from all of the photoelectric conversion elements and the radiation signal accumulation time XT (exposure time XT) is greater than the imaging interval FT of a synchronization signal. That is, this is an imaging mode in which the frame rate is relatively high, in which the shift registers on each rectangular semiconductor substrate are scanned to perform a resetting operation for starting accumulation of radiation signals at the time point indicated by t9 in FIG. 5B during an output period of an analog signal. If, however, a resetting operation is performed during an analog signal scan, currents simultaneously flow in all of the pixels on the rectangular semiconductor substrate to cause fluctuations in the power supply voltage of the rectangular semiconductor substrate. That is, an analog signal output during a resetting operation is disturbed to produce artifacts in a moving image.
The present invention provides a technique of obtaining a high-quality image by reducing artifacts even in a high-speed imaging mode, in consideration of the above problem.